The Intimate Bond Between Humans and Insects

‘Something in the insect seems to be alien to the habits, morals, and psychology of this world, as if it had come from some other planet, more monstrous, more energetic, more insensate, more atrocious, more infernal than our own.’

—Maurice Maeterlinck, Belgian playwright, 1862-1949

Such animosity hardly seems justified. Of the approximately 9 million species of insects on Earth—the vast majority undiscovered and unnamed—only about 11/2 percent do us any harm. The rest have either no direct impact or provide some very obvious and indispensable benefits to humans. They pollinate plants, including 80 percent of the world’s 94 major food crops, as well as vast tracts of tropical rain forest. They decompose our dead and all the waste that animals and plants produce, from dung to discarded skin, feathers to hair, dead leaves to rotten wood. They protect our harvests by eating the pests and the weeds that would destroy them. They are food for birds, frogs, reptiles, fish, and mammals—including, wittingly and unwittingly, humans. They aerate and enrich the soil by digging tunnels and carrying nutrients down from the surface. That, in turn, helps prevent erosion and runoff into rivers and streams.

MOSQUITO

It isn’t hard to understand why the mosquito is so reviled. Elegant, dainty, and deadly, it is the most common of all blood-sucking arthropods and the most important insect carrier of human disease, transmitting not only malaria but also yellow fever, dengue, West Nile virus, encephalitis, and the tiny worms that cause elephantiasis. But mosquitoes, with 3,550 species, have their place in the web of life. Birds, bats, fish, and many significant wetland species, including dragonflies, feed on them. Anopheles mosquitoes—among them A. stephensi, shown here—have arguably changed the course of human history. Over the centuries they have killed untold millions with the aid of the malaria parasite, Plasmodium, which they inject into blood along with their saliva. Prior to the widespread use of quinine, in fact, it was mosquito-borne malaria that largely protected Africa from European colonists, who died from the disease in such high numbers that the west coast of Africa was dubbed the white man’s grave. Another species, Aedes aegypti, carried yellow fever to the New Worldwith the African slave trade and helped drive France to negotiate the Louisiana Purchase in 1803.

If all insects were to suddenly vanish overnight, says Harvard biologist Edward O. Wilson, it’s likely humans would be endangered. All the plants that insects pollinate would disappear. All our detritus would pile up to colossal heights. Even the oceans would be affected. Nutrients would pour down off the increasingly denuded land into the sea, triggering massive algal blooms, which would exhaust the water of oxygen and threaten fish. And the impact on terrestrial ecosystems would be enormous. “If insects were gone, you would break a large part of the terrestrial food chain,” says Wilson. “A number of birds would starve in no time at all. Those birds and other animals that depend on birds for food would disappear. Small mammals in the soil that depend, in part, on insects would disappear. It would be a catastrophic chain reaction around the world.”

No one expects insects to evaporate into the ether, of course. But if insects had not evolved, humans probably wouldn’t exist either. That’s because the flowering plants on which we ultimately rely for nearly all our food came into dominance along with winged insects just after the extinction of the dinosaurs 65 million years ago. “A large portion of the flowering plants, or angiosperms, depended on the insects for pollination, and insects were a major factor in creating the soil conditions on which the plants grew,” Wilson says. “Humans came out of mammals, and mammals came out of vertebrates that were totally dependent on the flowering plants—grasslands and forests and so on. If insects had never originated, I’d say there’s virtually no chance that humans would have evolved as we know them. If an intelligent creature had evolved, it would probably not have been humanlike.”

Insects are far less dependent on us than we are on them. There is, however, a small subset of insects that would probably not exist, in their present form or state of superabundance, if humans did not provide them with a ready food supply. The universally despised cockroach, for example, has followed humans (and their trail of crumbs) to the ends of the earth and beyond: One was even spotted scurrying around on the Apollo XII spacecraft. The females of as many as 85 species of Anopheles mosquito suck human blood in order to nurture their eggs, often transmitting the protozoan malaria parasite, Plasmodium, in the process. Body lice, Pediculus humanus corporis, probably took up residence in garments only after humans began wearing them around 72,000 years ago, while their relatives Phthirus pubis, crab lice, live among human pubic hairs and rarely anywhere else. The common bedbug Cimex lectularius—known as “the sex maniac of the insect world” for its insatiable lust—probably evolved in caves as a parasite of bats or birds before it began feeding on human blood. Other insects, such as locusts, granary weevils, and aphids, found a profitable niche when humans invented agriculture 10,000 years ago and grain storage some 5,500 years later. And houseflies, carpet beetles, silverfish, and various species of moths and fleas have all set up home with humans.

At the same time, we have exploited insects—for honey, beeswax, silk, and various, usually dubious, forms of medicine. We have also seen them as a source of inspiration: The Egyptians symbolized their sun god, Ra, as a great scarab beetle rolling the sun like a ball of dung across the heavens. Even the much-detested mosquito is held up as an example in the Talmud. “Why was the mosquito created before man?” it asks. “So that if man becomes haughty, he can be deflated by being told, ‘The mosquito came before you.’”

Insects—which, like humans, make music, communicate in symbols, grow subterranean crops, enslave each other, and even fight wars—have also stirred the human imagination, giving rise to everything from the band name The Beatles to Franz Kafka’s immortal hero Gregor Samsa, who awakes one morning to find himself transformed in his bed into a gigantic insect. Instead of reaching for the bug spray, then, why not celebrate our bond with insects? As the venerable Jules Michelet wrote in his 1858 epic, The Insect, “We are truly somewhat akin. For what am I myself, but a worker? What has been my greatest happiness in this world?”

A dead body is a banquet to corpse-eating insects. Calliphora vicina, the blowfly seen hatching here from its pupa (above), is often the first to alight at the table of death, drawn by fresh flesh scented with acids and gases that signal the onset of decay.

So sensitive are this insect’s eyes and antennae that it can spot a body when flying more than 115 feet above it. But breeding, not eating, is the adult blowfly’s aim: The female lays tiny eggs (below) in patches around orifices such as the nose, ears, and eyes and also on open, bloody wounds. The maggots into which they hatch burrow into flesh, exuding enzymes that can digest fats and collagen, a protein found in skin tendons and cartilage. Ugly though they may be, blowflies benefit humans by decomposing debris.

They are also of serious interest to forensic scientists, who can estimate the time of death—and thus help solve crimes—by examining the insects that settle on a corpse. That’s because insects visit a body in discrete waves for months or years if a body is left unburied. For example, forensic entomologist Gail Anderson of Simon Fraser University in Burnaby British Columbia, helped solve a poaching case by examining fresh blowfly eggs laid on twin bear cubs that had been shot and gutted for their gallbladders, a prized ingredient in some Asian medicines. By watching the eggs until they hatched, she could pinpoint the time they had been laid—on an evening when two suspects had been seen near where the bears’ bodies had been dumped. Her evidence helped send the two men to jail.

Honeybee

Humans have been helping themselves to honey and beeswax for at least 3,000 years, when they first domesticated the bee. Apis mellifera—seen here above as it hatches from a honeycomb—provides other benefits: About one-third of the human diet is derived from bee-pollinated crops. Were bees to become extinct, we would most likely lose almonds, oranges, apples, blueberries, eggplants, tea, garlic, carrots, and onions, among many others.

Humans have exploited bees for other reasons. Bee venom has long been known to soothe arthritis, probably because it contains melittin, a potent anti-inflammatory agent. Honey itself is active against bacteria. Microbiologist Rose Cooper at the University of Wales has found honey to be 10 times more effective than a sugar solution at killing antibiotic-resistantStaphylococcus aureas, a wound-infecting bacterium common in hospitals, perhaps because honey contains plant chemicals that inhibit microbial growth.

The Drugstore Beetle

Why Not Eat Insects? is the title of a short polemic published in 1885 by Vincent Holt. In it he argued that insects were nutritious, delicious, and readily available. The only obstacle to their widespread consumption, it would seem, is the inbred disgust that many people feel at swallowing, say, sautéed silkworms or curried cockchafers.

In many parts of the world, however, bug eating is not only common but relished: In Thailand, for example, salted silkworm pupae are a delicacy, as are mangdana, or giant water bugs, which are often tossed into salads. Insects are, in fact, remarkably nutritious: According to data compiled by Iowa State University, 100 grams of grasshoppers contain about 20 grams of protein and only 6 grams of fat. Whether we admit it or not, though, we all eat bugs all the time—unknowingly. Insects such as granary weevils, meal moths, and spider beetles have been hiding in our food ever since the Egyptians invented grain storage 4,500 years ago—and so we often eat them too.

The drugstore beetle, Stegobiuim paniceum, seen here poking its head out from behind a bread crumb, feeds not only on flour, spices, and fish food but also on books, mildly toxic medicines, and even tin and lead sheets— “anything but cast iron,” as one wag put it. The Food and Drug Administration, recognizing the ubiquity of such insect pests, sets limits on acceptable levels of bugs rather than banning them completely from food. Pitted dates, for example, are condemned only if 5 percent or more of each batch are contaminated by dead insects or their excreta. Golden raisins arepermitted up to 35 fruit fly eggs per 8 ounces.

Body Lice

Three species of lice call humans their home: the crab louse, the head louse, and its descendant (pictured here, mating) the body louse, Pediculus humanus corporis, which lives in clothing, feeds on human blood, and leaves the body only when it cools, after death.

One famous louse host was Thomas à Becket, murdered in Canterbury Cathedral in 1170 by henchmen of England’s King Henry II. As his robe-swaddled body lay in state the next day, onlookers were alternately aghast, then convulsed with laughter, to see that “the vermin boiled over like water in a simmering cauldron.” Lice cannot survive in unworn clothing; hence, body lice are most common in crowded conditions like prison camps, where washing is infrequent.

That explains why the diseases they transmit in their feces—typhus, trench fever, and relapsing fever—occur so commonly in wartime. Typhus, a disease caused by bacteria called rickettsias, has been blamed for numerous military debacles, the earliest in 1489 when it killed 17,000 soldiers in a war over Granada between the Moors and the Spanish army of Ferdinand and Isabella. Further, typhus claimed so many millions of lives during the 1917 Bolshevik Revolution that it threatened to torpedo the newly born Soviet state, leading Lenin to exclaim, “Either socialism will defeat the louse, or the louse will defeat socialism.”

Carpenter Ants

“One day when I went out to my wood-pile,” wrote Henry David Thoreau in his classicWalden; or, Life in the Woods, “I observed two large ants, the one red, the other much larger, nearly half an inch long, and black, fiercely contending with one another.

Having once got hold they never let go, but struggled and wrestled and rolled on the chips incessantly.” Waging war is just one of the habits that ants share with humans: Many species live in large, well-organized societies, and others take slaves, herd aphids like cattle, and raise fungi for food in underground farms. Ants are also, according to biologist Edward O. Wilson, the premier turners of soil in the world, the chief predators of other insects, and the principal scavengers of small dead animals—all activities that ultimately benefit humans. Camponotus floridanus, the Florida carpenter ants fighting here—one has locked its mandibles on the other’s antenna—share something else with humans: their homes.

Living in large tightly knit communities within nests hollowed out in wood softened by moisture or fungi, these ants are fond of sweet fluids, and during the night they often scavenge for sugary juice around soda machines. Their nests are common in attics, closets, and fuse boxes, to which they gain access by following chemical trails along wires or branches that form bridges to safe spots under the roof.

Bedbug

For much of human history the bedbug has been hard to dislodge.

“It is said to have its origin in warm blood, and has an extravagant fondness for humans,” wrote the 14th-century Egyptian theologian Kamal ad-Din ad-Damiri. He was mistaken about its origins: The common bedbug, Cimex lectularius, emerges by night from the walls of houses or bedding to quaff the blood the insect needs to molt from nymph to adult. It does, however, appear to have been our companion since we first took to dwelling in caves: At least 12 species of blood-sucking Cimex bugs are parasites of bats, and many others feed on cave-nesting birds.

Once driven away by DDT, the bedbug seems to be making a comeback, fueled by the trade in old flea-market furniture. Though it does not transmit disease, excessive biting can cause anemia in infants. The ancients inexplicably awarded them medicinal powers. The Roman Pliny the Elder, for example, recommended them for snakebites. “Seven bed bugs mingled with water were a dose for a man, while four were sufficient for children,” writes Glenn Herrick in his 1914 bookInsects Injurious to the Household and Annoying toMan, “The smell of them will [also] relieve ‘hysterical suffocation.’”